The invention concerns a magnetic resonance apparatus with a superconducting magnet coil which is disposed in a cryostat, and a refrigerator for cooling the magnet coil, which comprises a compressor for compressing a working gas, a high-pressure line and a low-pressure line between the compressor and a control valve that periodically connects the high-pressure line and the low-pressure line to a connecting line between the control valve and a cold head of the refrigerator, thereby generating pressure pulses through the switched working gas, wherein the control valve is mechanically rigidly connected to the cryostat.
A configuration of this type is disclosed by T. Tomaru et al. in Cryogenics 44, pages 309-317 (2004). The compressor is disposed outside of the cryostat and connected to the control valve via the high-pressure or low-pressure line. In order to reduce transmission of vibrations from the surroundings to the cryostat, in particular, to decouple the cryostat from the compressor, the high-pressure line and the low-pressure line are designed as flexible hoses through which a working gas is guided from the compressor to the control valve and finally to the cold head of the refrigerator. However, the vibrations of the pressure wave of the working gas within the lines cause the flexible conduit hoses to vibrate and transmit these vibrations to the control valve and therefore also to the cryostat. The vibrations may produce artifacts in the NMR signals.
It is therefore the underlying purpose of the invention to propose a magnetic resonance apparatus which supplies a working gas to a cold head using a compressor, such that the artifacts in the NMR signals caused by the above-described vibrations are minimized.